Siuslaw SWCD Knotweed

Japanese Knotweed is primarily a riparian species that was introduced to the Siuslaw Watershed in the early 1900ís as an edible/ornamental plant. Knotweed forms dense monocultures on stream banks, crowding out native vegetation and threatening aquatic health. Knotweed becomes dormant during the winter months, leaving stream banks bare of vegetation which increases the potential for erosion Each season as knotweed comes out of dormancy the patch size increases displacing more beneficial native vegetation.

The District has worked to eradicate knotweed over the last seven years. During 2009-10 we were able to visit sites treated in previous years and add sites lower in the selected watersheds. The results from treating sites in 2009-10 have significantly reduced knotweed patches. We have found that smaller patches under 100 square feet are often eradicated in one treatment while larger patches must be revisited in subsequent years to be successful. At Indian Creek, Sweet Creek, North Fork Siuslaw, Maple Creek, and Fiddle Creek we have been very successful at reducing the knotweed infestation and it is getting more and more difficult to find knotweed in these sub-watersheds.